Manufacture of rayon



Patented May 2, 1933 f 23: 1

UNITED semeenoacn a. LOCKHART, or rnovrnnn'cn, anoint ISLAND, Assrenon To Mimi annoxns comm, or rnwrucxnr, Rnonn} ISLAND, ei cor rone'rlon or an ISLAND MANUFACTUREl oh Bayes. I it No Drawing. Application filed April 17,

The present invention relates to an improved process for the production of artificial silk or rayon from viscose.

The invention has forv its principal object to provide a novel and improved process for desulphurizing and bleaching the viscose in one operation without at the same time forming compounds which will be injurious to the finished material.

In the manufacture of rayon by the viscose method, it has been found necessary to subject the unfinished material to a desulphurizing bath to remove certain impurities which consist largely of sulphur and sulphur compounds. The material is then washed and bleached, and is then subjected to further washings and treatments to remove any compounds remaining which may be detrimental to the fibre.

In accordance with the process commonly used, the fibre after being wound into skeins is washed and dried and then subjected to the action of a desulphurizing bath which comprises a solution of sodium sulphide and caustic soda or some similar alkaline solution. This solution acts to dissolve out the impurities inthe fibre consisting primarily of sulphur or sulphur compounds, either directly or by first changing these impurities into compounds which are soluble. The material is then taken from the desulphurizing bath and washed.

The material is now subjected to the action of a bleaching bath, the bleaching agent being chlorine liquor which acts by the liberation of oxygen to thoroughly bleach the material. Finally, the material is taken from the bleaching bath and is again washed and given certain treatments to remove any excess of alkali or acid or chlorine compounds remaining in or on the fibre.

Up to the present time, it has been considered impossible to desulphurize and bleach the material simultaneously. This is due primarily to the fact that the chlorine liquor solution either directly or indirectly, on account of the action of the liberated oxygen on the free sulphur and sulphur compounds to be found in the material, and also 'on account of the lime compounds contained in 192s. seri'aljlil' o. ssaeesl-lff thechlorine 'solution,' decomposes and come bines withimpuriti'es inthe silk to form hy"- drochloric, sulphurous and sulphuric" acids.

These-acids are extremely difficult to wash out of the silk and act whenithe material] is dry sooner 'or laterto eat into; the fibre so asto make it tenderand destroy its utility.=. In order to prevent this condition, it 'is-there-' fore usual to desulphurize the silkso far-as possible, reducing the sulphur impuritiesin the material tto-a minimum beforefit is-"subjected to the b'leaching operation; In carrying Ollt'th present invention, a method has beenprovided for combining the processes of desulphurizing and bleaching the viscose in one operation without at the sametimefforming compounds which willbe' injurious tothe finished material; The api plicant has discovered that by the usetf hydrogen peroxide in. an alkaline bath containing sodium'silicate, the processesof de-. sulphurizing and bleaching can be' c'arr'ied' outsimultaneously, thereby eliminatingcomplleifely one process in the treatment of the s1 Apparently, and so far as the applicant can determine, one of the reasons for the success of this method of desulphurizing and bleaching the viscose fibre in one operation is that the hydrogen peroxide is a very active oxidizing agent andgives off great quantities of oxygen very rapidly, particularly when the temperature is raised. This oxygen'ap- I parently combines with the free sulphur and sulphur compounds of the fibres to form soluble sulphur salts without any marked tendency towards the formation of sulphurous, sulphuric or other injurious acids. Inasmuch as there is no chlorine liberated either directly or indirectly during the reaction, there is, of course, no tendency towards the formation of hydro-chloric acid. Another reason for the success of the method is apparently that the sodium silicate facilitates the action of the liberated oxygen in forming soluble sulphur salts without the formation of injurious acids, the sodium silicate constituting a reagent capable of reacting with the liberated oxygen and the sulphur and sul phur compounds of the fibre to eliminate in: =-ipregentdnvention centemplatesihe: usgiof I I moxidizingagentsw-oizher'wthamhydrogen-1' 1':"nfiwhyperoxiide and-reagents'otheritharr sodium ;silicate,iorbaths-other;thanthcsedistincfly- H alkalingproviding thatlthe' reagentbr-baflr- ;:nrmmisicapable-:afireactingwith'the'libemtedk aZ:.1t0theactionzofhydrcgenperoxideinanalka-.' i

-j-;linebath.containingadditionallysodiumsiliw.-=:-: him I w cate.

In testimony whereof I have signed my name to this specification.

GEORGE R. LOGKHART. 

